In the Fortin barometer, the level of mercury in the glass at the bottom of the barometer cistern is adjusted to a scale zero, known as the fiducial point, each time a reading is to be taken. The level of mercury in the column is then read against the scale, using a vernier adjustment for extra accuracy. Air is evacuated from the top of the tube of mercury and the lower end is fixed in the cistern containing the reservoir of mercury. The Fortin barometer is simple to use as it has a clear easy-to-read linear scale. These barometers can be mounted on a wall or suitable pillar.
In addition to instruments manufactured under the Russell Scientific Instruments' name, we manufacture, service and repair F Darton and WF Stanley, Griffin and George, and Gallenkamp precision mercury barometers.